The author's aim is simple: it is to demonstrate that the Scriptures teach that the dreaded Mark of the Beast is nothing Gentile Christians should fear.
Rather than it being forced upon Christians worldwide, he suggests its effect is limited to Jews in Judea.
It is to be a problem for those who are to worship God in the Jerusalem temple, with sacrifices and offerings. Some will be tempted to take the mark and worship and idol to be set up in that temple.